Method for eliminating degradation of crossed-field-amplifier performance

ABSTRACT

A method for restoring the performance of certain crossed-fieldamplifier tubes which have deteriorated because of degradation of the secondary emission characteristic. Performance is restored by providing an agent for gettering desorbed carbon on the cathode and activating the tube and the gettering agent simultaneously.

ilnited States Patent 11 1 CROSSED-FHELD-AMPLIFIER PERFORMANCE Inventor: Bernard Goldstein, Princeton, NJ.

Filed: Feb. 3, 1972 AppL No.5 223,327

US. Cl. .Q 316/2 Int. Cl. H01j 9/50 Field of Search 316/25, 2; 313/174, 178

References Cited UNITED STATES. PATENTS Wagener 313/174 Goldstein Mar. 5, 1974 METHOD FOR ELIMINATING 2,926,981 3/1960 Stout et al. 316/25 1 DEGRADATION 01: 3,100,274 8/1963 Luftman et a1. 313/178 Primary Examiner-Roy Lake Assistant Examiner--J. W. Davie Att0rney,'Agent, or Firm-R. S. Sciascia; J; W. Pease; J. F. Miller [57] ABSTRACT A method for restoring the performance of certain crossed-field-amplifier tubes which have deteriorated because of degradation of the secondary emission characteristic. Performance is restored by providing an agent for gettering desorbed carbon on the cathode and activating the tube and the gettering agent simultaneously.

2 Claims, N0 Drawings 1 METHOD FOR ELIMINATING DEGRADATION OF CROSSED-FlELD-AMPLIFIER PERFORMANCE BACKGROUND OF THE INVENTION Certain crossed-field-amplifier tubes suffer a loss of performance which increases with time of operation. It has been found that this loss of performance is caused by degradation of the secondary emission characteristic 8. It had been believed heretofore that the degradation of 8 was caused by a deactivation by some unknown mechanism of the surface properties of the cathode. It had also been known that a degraded CFA tube can be restored by the continuous admission of oxygen into the tube from a heated Cu O source. It was thought that in some unknown way the oxygen reactivates the cathode surface. Applicant has overcome this problem of the prior art by discovering the mechanism actually involved and providing means and a method for preventing the degradation of crossed-fieldamplifier tubes.

SUMMARY OF THEYINVENTION Applicant has discovered that the deterioration of 8 in crossed-field-amplifier tubes is caused by the presence of carbon as a contaminant on the surface of the cathode. A practical means and method for removing the carbon contaminant by gettering with titanium is provided.

DESCRIPTION OF THE PREFERRED EMBODIMENT It has been discovered that the deterioration of performance in some crossed-field-amplifier tubes is caused by degradation in the secondary emission characteristic 8. The characteristic is defined as the ratio of total (secondary) current emitted from a surface to total (primary) current incident on the surface. It had The inventor has discovered that the loss of 8 in a CPA tube is not. caused by a deterioration of the surface properties of the cathode as had been thought, but by a contamination of the cathode surface due to the presence of carbon. By using Auger spectroscopy as a means for identifying and qualitatively measuring trace impurities on a metallic surface the inventor has discovered a direct relationship between the amount of carbon on the cathode surface and the secondary emission characteristic 5. The inventor has discovered also that the electron beam in a CPA tube is directly responsible for the selective desorption of carbon from the surface. During the electron bombardment of the cathode the area under the beam, and only under the beam, desorbs carbon. The admission of oxygen is by itself insufficient to remove (desorb) carbon from the cathode and restore 8.

The invention provides a quantity of titanium in the tube to getter the carbon desorbed from the cathode surface by the electron beam. After a crossed-fieldamplifier has been operated a considerable length of time such that its performance has deteriorated because of the progressive degradation of the secondary emission characteristic, the tube is activated and the titanium therein is activated simultaneously. Activation of the tube causes an electron beam to strike the cathode. The electron bombardment causes a desorption of carbon from the cathode surface. Activation of the titanium results in a gettering of the carbon so that it cannot recombine with the cathode surface, thus restoring the secondary emission characteristic of the cathode and the efficiency of the tube. By activating" the tube is meant turning on or operating the tube. Activating the titanium means flash-evaporating a quantity of titanium in the tube or freshly exposing the titanium on a filament by suitably heating the filament which is titanium coated. These techniques are well known in the art. See US. Pat. Nos. 2,926,981; 2,948,607; and 3,100,274.

Gettering with metals such as titanium is well known. It is known that titanium is an effective getterer for carbon in the form of CO and CO It is common practice in the art to place a gettering material in vacuum tubes to remove traces of unwanted gasses such as air, oxygen, water vapor, etc., which cannot be removed during manufacture. It is known to provide gettering materials in tubes to getter unwanted elements released during operation. It is known to include a titanium or parttitanium electrode in a vacuum tube to provide a gettering action.

What has not been known heretofore andwhat applicant claims as his invention is the discovery that the progressive deterioration of performance of crossedfield-amplifier tubes occurring with continued use is caused by a progressive build-up of carbon on cathode and that this carbon can be removed and the tube restored by desorbing the carbon from the cathode surface with an electron beam in the presence of activated titanium getter. The following claimsare so limited.

What is claimed is:

1. The method of restoring a used crossed-fieldamplifier tube wherein the secondary emission characteristic 5 of the cathode of said tube has deteriorated because of an accumulation of carbon on the surface of said cathode, comprising the steps of:

placing a quantity of titanium, additional to any gettering agent used to remove residual gasses when the tube is manufactured, in said tube at a convenient time, activating said tube after its secondary emission characteristic has deteriorated, to bombard said cathode surface with an electron beam, and

simultaneously applying suitable heat to freshly expose said additional titanium when said tube is activated to getter the carbon desorbed from the surface of said cathode by said electron beam.

2. The method of removing carbon from the surface of the cathode of a used crossed-field-amplifier tube comprising the steps of:

placing a quantity of titanium in said tube, additional to any gettering agent used to getter residual gasses, during manufacture,

activating said tube to bombard said cathode with a beam of electrons after said tube has been operated a length of time sufficient to incur a deterioration of the secondary emission characteristic 8, and simultaneously suitably heating said titanium to produce a freshly exposed layer to vgetter any carbon desorbed from said cathode surface by said beam of electrons. 

2. The method of removing carbon from the surface of the cathode of a used crossed-field-amplifier tube comprising the steps of: placing a quantity of titanium in said tube, additional to any gettering agent used to getter residual gasses, during manufacture, activating said tube to bombard said cathode with a beam of electrons after said tube has been operated a length of time sufficient to incur a deterioration of the secondary emission characteristic delta , and simultaneously suitably heating said titanium to produce a freshly exposed layer to getter any carbon desorbed from said cathode surface by said beam of electrons. 